envsetup.sh: add 'syswrite' function

This function:
- disables verity on the device
- reboots the device only if it is needed
- remounts partitions on the device

Bug: 167697453
Test: syswrite
Change-Id: I23c3e88daaa2b334233f4faf7fe8f8244cd56225

envsetup.sh

@@ -34,6 +34,7 @@ Invoke ". build/envsetup.sh" from your shell to add the following functions to y
 - gomod:      Go to the directory containing a module.
 - pathmod:    Get the directory containing a module.
 - refreshmod: Refresh list of modules for allmod/gomod/pathmod.
+- syswrite:   Remount partitions (e.g. system.img) as writable, rebooting if necessary.
 
 Environment options:
 - SANITIZE_HOST: Set to 'address' to use ASAN for all host modules.
@@ -857,6 +858,18 @@ function qpid() {
     fi
 }
 
+# syswrite - disable verity, reboot if needed, and remount image
+#
+# Easy way to make system.img/etc writable
+function syswrite() {
+  adb wait-for-device && adb root || return 1
+  if [[ $(adb disable-verity | grep "reboot") ]]; then
+      echo "rebooting"
+      adb reboot && adb wait-for-device && adb root || return 1
+  fi
+  adb wait-for-device && adb remount || return 1
+}
+
 # coredump_setup - enable core dumps globally for any process
 #                  that has the core-file-size limit set correctly
 #